1. Field of the Invention
The invention relates to voltage regulation devices in general and more specifically to voltage regulation in power supplies feeding pulsed loads.
2. Description of the Prior Art
In the prior art, the engineering problem of controlling, stabilizing or regulating a high-voltage source has been variously addressed. In pulsed-load applications (for example, in radar systems), a source of high-voltage direct current is usually required, and a pulse modulator or electronic switching device develops a high-voltage, high-energy pulse therefrom which is used to energize a magnetron, amplitron, traveling wave tube or similar microwave oscillator or amplifying device.
The type of pulsed load aforementioned can require very high peak power, although in view of the relatively low duty cycle of devices such as pulsed radar transmitters, the average power is a relatively small fraction of the peak power. Accordingly, power supply components which would be capable of supplying the peak powers over an appreciable period of time are not used, since the disadvantages from a point of view of energy efficiency, cost and weight require the use of power supplies capable of supplying little more than the average power, these having relatively high internal impedance and relying on filter/storage capacitor arrangements to supply the peak power.
In some radar applications as, for example, when so-called moving target indicator circuits (MTI) are being used, the phase coherence of the transmitted signal must be preserved. Since the hereinbefore referred to RF generators and amplifiers are sensitive to the modulating pulse amplitude in respect to RF phase coherence, it is important that the initial or starting point during each transmitted pulse be repeatable. If it is, at least some "droop" can be tolerated thereafter, since this tends to be consistent and repeatable if the starting, instantaneously applied pulse voltage is repeatable from one pulse to the next.
In radar systems of the type, direct bootstrap regulators have been applied and are known per se in this field. Such direct bootstrap regulators are subject to transients because of arcs or flashovers, which may produce discharge currents of 1000 amperes or more and energy levels in the thousands of joules in systems of considerable radio frequency power-generating capability. Such transients are extremely difficult to isolate from the direct bootstrap device. In the past, the designer has been obliged to use vacuum tubes of large peak current-carrying capability and/or complex filters, bypasses and protective circuitry.
In such conventional or prior art bootstrap circuits, the filter/storage capacitor is fed by a first-order-regulated power supply, the ground end of the filter/storage capacitor thereof being connected through an active element such as a series of vacuum tubes. An error-sensing circuit then grid-drives the vacuum tubes which provide their function by varying the effective resistance in the capacitor current path.
Ordinarily, the first order or coarse-regulating circuits employed may be of a prior art type, such as a pulse-width-controlled inverter type, or the like. The coarse-regulator circuit per se is not able to provide voltage control closer than about .+-.30 volts when the high voltage itself is on the order of 50,000 volts, although closer, long term regulation is not technically impossible, albeit impractical.
The manner in which the present invention improves upon the state of the art in bootstrap regulators will be evident as this description proceeds.